------- Comment #1 from grosser at gcc dot gnu dot org 2008-10-16 05:20 ------- Created an attachment (id=16505) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16505&action=view) Fix loop_affine_expr to remove limit_scops () - This is a HACK looking for smarter solution
Problem 1: Scalar evolution functions in loop limits and conditions have to be constant or affine to be allowed in a SCoP. During SCoP detection we check this with: if (evolution_function_is_invariant_p (scev, n) || evolution_function_is_affine_multivariate_p (scev, n)); in loop_affine_expr(). If this expression is true, it is allowed in a SCoP. But e.g. the constant expr "p_1 * p_2" is allow in a SCoP, but we can not represent it using the polyhedron model. The matrix would be p_1 p_2 Const x y z with x*p_1 + y*p_2 + z There is no way to represent p_1 * p_2, so we fail in scan_tree_for_params trying to generate the matrix. There are two solutions: 1. This expression is representable, if we introduce a new parameter p_3 = p_1 * p_2 and calculate it before the SCoP. 2. We detect this cases and do not allow them in any SCoP. I would like to start with solution two. Later on we can implement solution one. I attached a patch, that simply copies scan_tree_for_params() and returns true, if a expression can be handled by scan_tree_for_params() otherwise false. This works on polyhedron using -fgraphite, but seems not to be the cleanest solution. I would prefer to keep if (evolution_function_is_invariant_p (scev, n) || evolution_function_is_affine_multivariate_p (scev, n)); and add only && (no_multiplication_in_parameters (scev)). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37705